an half eaten apple burnt onto my screen!!

iv'e been using my ibook for about 4 dayz now, and just this morning, i opened it up to turn the screen on and i saw that the little apple logo was "burnt" onto the middle of the screen. is this normal?? did i do something wrong to make this happen??

Actually, that's not entirely true, at least in my own experience. We use LCD's exclusively at my office, and a few of them remain on 24/7 with certain images that are unchanging. If the image is moved and a neutral background is present, you can see faintly where the image was.